1010] 



on Magnetic Storms. 



11^ 



visible between sun-spot frequency and the regular diurnal inequality 

 becomes more and more obliterated as we pass from the regular 

 to the less regular, and from these to the highly irregular daily 

 changes of terrestrial magnetism. This phenomenon is capable of 

 several explanations. The regular and irregulai changes of the 

 magnetic elements may be mainly due to distinct causes, and the 

 irregular changes may have little if any dependence on the condition 

 of the solar surface. On the other hand, sun-spots of similar area 

 may be of widely different character. There may in short l)e only 

 an occasional Napoleon among sun-spots capable of producing large 

 magnetic disturbance on the earth: and mere areas or frequencies 

 may possess little or no significance in this connection. A third 

 possibility is that the magnetic condition on any one day depends on 

 the solar condition of a considerable number of previous days. 



§11. A general parallelism between sun-spot frequency and the 

 range of the regular diurnal inequahty, such as appears in Table VII., 

 is far from proving any intimate connection between the two phe- 

 nomena on the same day. Table VIII. gives the results of an attempt 

 which I made to find out whether the parallelism extends to indi- 

 vidual days' results. 



Table VIII. 



Relation of Sun Spot Area (Greenwich) to Absolute Declination 

 Range (Kew) on Same Day and on Three Subsequent Days. 



Algebraic Kxcess of Declination Range Over Mean from all Days. 



The days of each month were divided into three groups. The 

 first group included the 10 days in which the Greenwich sun-spct 

 areas were the largest, the third group the 10 days in Avhich they 

 were least. If any close parallelism existed between the solar and 

 magnetic phenomena on the same day, we should expect the mean of 

 the absolute declination ranges from the first group of days to be 

 much larger than the mean for the whole month, and that from the 

 third group to be much less. Taking all the months of the years 

 1890-r.)0u, there is a difference in the direction indicated, but it is 



